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A J Griffiths

Publications and source records attributed to A J Griffiths.

At least 37 records · Page 2Linked to original sources
PubMed1994

New mutations that suppress mating-type vegetative incompatibility in Neurospora crassa.

The mating-type locus in the ascomycete Neurospora crassa functions as a vegetative-incompatibility locus during asexual growth such that A+a heterokaryons and A/a partial diploids are inhibited in their growth. In this study, we sought mutations that suppress mating-type associated vegetative incompatibility by using A/a partial diploids. Mutants were selected as spontaneous escapes from inhibited growth. Suppressors were identified by selecting escapes that retained the capacity to mate with both A and a strains. The escaped partial diploids were then outcrossed to remove the duplication. Seven suppressors were identified that segregated as single, recessive mutations. All seven of the suppressors were shown to be allelic to a previously obtained suppressor, tol, by segregation analyses and heterokaryon tests. This result indicates that all seven mutations are new alleles of tol and suggests that tol is a key regulatory locus in the expression of mating-type associated vegetative incompatibility in N. crassa.

Alleles↗
PubMed1993

Transcription of the kalilo linear senescence plasmid from Neurospora intermedia.

The 8.6-kb kalilo linear mitochondrial plasmid of Neurospora intermedia was found to give rise to multiple transcripts of 8.6, 4.4, 4.0, 1.3, 1.2, and 0.9 kb. Plasmid transcripts were found in all the developmental stages tested and were present in cells with and without plasmid integration into mtDNA. The 4.4- and 4.0-kb transcripts corresponded to the two known ORFs in size, position, and polarity. An analysis of RNA fractions has confirmed the mitochondrial location of kalilo. The kalilo-specific RNA appears to be selectively unstable in affected strains of N. intermedia; this may be a general property of linear plasmid RNA. Transcripts are most likely initiated from near the termini of the linear plasmid. Primer extension and sequencing showed a clear 5' RNA end at nucleotide 101. However, the sequence in this region does not show homology with any known mitochondrial, plasmid, or nuclear promoter. The sequence does show homology with the tip of the plasmid and marks the border of a long series of direct repeats. Possibly the plasmid RNA polymerase may be bifunctional, recognizing sequences at the plasmid tip as well as the promoter.

Base Sequence↗
PubMed1993

Plasmid diversity in senescent and nonsenescent strains of Neurospora.

A sample of 171 natural isolates of Neurospora crassa and Neurospora intermedia was tested for senescence. Of these, 28 strains senesced within the duration of the experiment. These senescent strains, together with a selection of nonsenescent strains, were examined for the presence of mitochondrial plasmids. This was done by digesting mitochondrial DNA preparations with proteinase K, and running these samples on agarose gels. Most of the strains examined, both senescent and nonsenescent, contained plasmids, many of them new. Some new plasmids were linear, as inferred from their resistance to 5' exonuclease and sensitivity to 3' exonuclease. New circular plasmids were also found. Some strains carry several plasmids, and mixtures of circular and linear elements were common. A cross-homology study was performed on a sample of plasmid-bearing strains, and several cases of apparent relatedness were found, some between strains from distant geographical locations. Linear plasmids homologous to the maranhar linear senescence plasmid were quite common. A new member of the LaBelle circular plasmid homology group was found. In the sample tested for homology, no strains contained elements related to the kalilo linear senescence plasmid. The relationship of the new plasmids to senescence is not known. In addition to plasmid monomers, several different types of derivatives were found. The kalilo linear plasmid was found to occur in linear and circular forms of low mobility, presumed to be giant concatamers, and, in some strains, variant sibling structures and ladders of short derivatives were found. Circular plasmids also gave rise to extensive ladders on electrophoresis, probably representing different relaxation states and head-to-tail concatameric series. Some such forms migrated more slowly than mitochondrial DNA. One unique type of plasmid modification observed was a pair of linear elements that had apparently arisen de novo which showed homology to a circular plasmid.

DNA, Circular↗
PubMed1993

Male transmission of linear plasmids and mitochondrial DNA in the fungus Neurospora.

One of the general rules of heredity is that in anisogamous matings genetic elements in organelles are inherited maternally. Nevertheless, there are cases of paternal transmission, both as rare exceptions, and as regular modes of inheritance. We report two new cases of paternal transmission in crosses of the model fungus Neurospora. First, we show leakage of a linear plasmid from males, the first case in fungi and the second in eukaryotes. Transmission frequencies ranged from 1% to 15% in different crosses, but some crosses showed no detectable male transmission. Second, we show leakage of male mitochondrial DNA (mtDNA), the second case in fungi. Some of the resulting progeny have only the male mtDNA type, but some are heteroplasmons. Heteroplasmons show novel restriction fragments attributable to recombination or rearrangement. Heteroplasmy of mtDNA through male transmission has not been reported previously in any eukaryote. In addition we have shown paternal leakage of circular mitochondrial plasmids, supporting another reported case. In a male bearing a linear and a circular plasmid, these plasmids and the mtDNA are transmitted in different combinations. These results show a potential for mitochondrial segregation and assortment during the sexual cycle in anisogamous fungi, pointing to more potential avenues for novel associations between genomic compartments, and between genomic and extragenomic elements.

Crosses, Genetic↗
PubMed1993

Plasmid suppressors active in the sexual cycle of Neurospora intermedia.

We have discovered that, in certain crosses of natural isolates of Neurospora intermedia, linear and circular mitochondrial plasmids of the maternal parent are not transmitted to the progeny. This contrasts with the maternal transmission of organellar genetic elements generally observed in crosses between laboratory strains and between other natural isolates. Formally, failure of plasmid transmission is a type of plasmid suppression. The present cases represent the first report of plasmid suppressors in natural populations of fungi. Strains used as female parents can transmit or not transmit plasmids depending on the strain used as male parent. Males that act to suppress in one cross fail to suppress in others. Therefore, the suppression of plasmids depends on a strain-specific interaction and is not determined exclusively by the males. Since suppression is a specific interaction we inferred that it must be genetically based and tested this hypothesis by seeking segregation of suppressed and nonsuppressed phenotypes in octads. Segregation of the original full suppression of all plasmids was indeed observed in each of the three sets of testcrosses examined. The interaction type of suppression must be initiated in ascogenous tissue during the sexual cycle. It is a nonautonomous type of suppression, affecting all descendent cells. In any one case of suppression, either one, several, or all plasmids can be lost. Both linear and circular plasmids can be eliminated by the same suppressor genotype. In addition, several strains were found to contain suppressors that act after ascospore delineation. This autonomous type of suppression has been observed previously in laboratory strains, but not in natural isolates. All the cases of plasmid suppression identified in this study involved a range of apparently neutral circular and linear plasmids. Using one senescent Kalilo strain of N. intermedia, we did not detect any case of suppression of the senescence-determining linear plasmid kalDNA.

Crosses, Genetic↗
PubMed1992

Suppression of cytoplasmic senescence in Neurospora.

We have shown that senescence in Kalilo strains of Neurospora, caused by a linear mitochondrial plasmid called kalDNA, is suppressible by existing variants of the nuclear genome. The suppressors are manifested by 4:4 segregation of senescence and immortality in asci from crosses between senescent female strains and males chosen from non-senescent candidate stocks. In one case of suppression, the asci also show segregation at the plasmid level. There is a reduction of kalDNA to barely detectable levels in the four ascospores showing immortality, so this suppressor evidently influences the maintenance of the plasmid itself. In the other case of suppression, the phenotypic segregation is not correlated with segregation at the plasmid level, and all eight ascospores in the asci show both free and inserted forms of kalDNA. This suggests that the suppression genotype provides a way of tolerating the presence of the plasmid rather than diminishing it. However, the allele f, which provides an analogous kind of suppression for the cytoplasmic mutation poky, does not suppress Kalilo or Maranhar senescence. Suppression is hence shown to be a possible option for host strains to combat the plasmid in nature, but no examples of suppressors were found in a limited survey of natural isolates. In addition, we have shown that long-lived, presumably non-senescent, strains do not arise by suppressor mutation, but lose senescence plasmid DNA by another mechanism.

Cytoplasm↗
PubMed1991

A new senescence-inducing mitochondrial linear plasmid in field-isolated Neurospora crassa strains from India.

Several field-collected strains of Neurospora crassa from the vicinity or Aarey, Bombay, India, are prone to precocious senescence and death. Analysis of one strain, Aarely-1e, demonstrated that the genetic determinants for the predisposition to senescence are maternally inherited. The senescence-prone strains contain a 7-kb, linear, mitochondrial DNA plasmid, maranhar, which is not present in long-lived isolates from the same geographical location. The maranhar plasmid has inverted terminal repeats with protein covalently bound at the 5' termini. Molecular hybridization experiments have demonstrated no substantial DNA sequence homology between the plasmid and the normal mitochondrial (mtDNA) and nuclear genomes of long-lived strains of N. crassa. Integrated maranhar sequences were detected in the mtDNAs of two cultures derived from Aarey-1e, and mtDNAs with the insertion sequences accumulated during subculturing. Nucleotide sequence analysis of cloned fragments of the two insertion sequences demonstrates that they are flanked by long inverted repeats of mtDNA. The senescence syndrome of the maranhar strains, and the mode of integration of the plasmid, are reminiscent of those seen in the kalilo strains of N. intermedia. Nonetheless, there is no detectable nucleotide sequence homology between the maranhar and kalilo plasmids.

Base Sequence↗
PubMed1989

Linear kalilo DNA is a Neurospora mitochondrial plasmid that integrates into the mitochondrial DNA.

The linear autonomous form of kalilo DNA (previously called AR-kalDNA) is shown to be resident within mitochondria rather than nuclei, as had been suggested by previous experiments. This form has been renamed mtAR-kalDNA, to signify its mitochondrial location. Experiments are described that illustrate the inheritance and somatic transmission patterns of the mitochondrial kalilo plasmid and the mitochondrial inserted form of kalilo DNA (mtIS-kalDNA). Progeny of a cross with a pre-senescent subculture as the female parent inherited mtAR-kalDNA only; mtIS-kalDNA was not transmitted sexually. During somatic propagation of the ascospore cultures, novel kalilo DNA inserts appeared and most of them persisted until death. We propose that these inserts originated from de novo integration of mtAR-kalDNA into the mitochondrial DNA. In two of the ascopore-derived series analyzed, the first inserts detected were seen only transiently and inserts appearing subsequent to the transient inserts were retained until death. We propose that these enduring inserts originated either from rearrangements of the transient inserts or from novel integration events, either from mtAR-kalDNA or from transposition of the transient inserts.

Blotting, Southern↗
PubMed1988

Double stranded RNA in natural isolates of Neurospora.

Thirty-six wild type isolates of Neurospora were surveyed for the presence of dsRNA. The survey identified seven strains which contain dsRNA molecules. These seven strains are all from different geographic locations. The sizes of the dsRNAs range from 500 bp to 18 kb and a total of seven distinct dsRNA species was identified. Cross homologies of some of the dsRNAs were apparent. There was homology between the 9.0 kb dsRNA and genomic DNA prepared from all strains in the survey, indicating a possible cellular rather than viral origin for this dsRNA species. None of the other dsRNAs hybridized with genomic DNA suggesting a viral origin for these dsRNAs.

DNA, Fungal↗
PubMed1986

An extrachromosomal plasmid is the etiological precursor of kalDNA insertion sequences in the mitochondrial chromosome of senescent neurospora.

In the kalilo strains of N. intermedia, senescence is initiated by insertion of a 9.0 kb foreign nucleotide sequence, kalDNA, into mitochondrial DNA. A 9.0 kb linear DNA plasmid that is structurally homologous to the mitochondrial kalDNA insertion sequences exists in high copy numbers in close association with the nuclei of presenescent and senescent kalilo cells, but is not present in cells of long-lived normal strains. The free kalilo plasmid has not been detected in mitochondria, suggesting that the element does not contain a mitochondrial origin of replication. Unexpectedly, the nuclear plasmid, like the mitochondrial insertion element, follows a strict pattern of maternal inheritance. We surmise that the extramitochondrial plasmid is the etiological precursor of the kalDNA insertion sequences that appear in the mtDNAs of senescent cell lines and conclude that the kalilo element induces senescence because it is a mutator of mitochondrial genes.

DNA Replication↗
PubMed1985

Insertion of a foreign nucleotide sequence into mitochondrial DNA causes senescence in Neurospora intermedia.

The kalilo variants of Neurospora contain a cytoplasmic genetic factor that causes senescence. This factor is a 9.0 kb transposable element (kalDNA) that lacks nucleotide sequence homology with mtDNA and is inserted into the mitochondrial chromosome, often at sites located within the open reading frame in the intron-DNA of the mitochondrial 25S-rRNA gene. Genomes containing the "foreign" DNA insert accumulate during growth, and death occurs as the cells become deficient in functional large and small subunits of mitochondrial ribosomes. The kalDNA transposon may be an "activator" element that causes breaks in mtDNA. Nonsenescing [+] strains of Neurospora do not contain kalDNA.

Base Sequence↗
PubMed1985

Enzyme composition and the taxonomy of Acanthamoeba.

The enzyme activities of 37 representative strains of Acanthamoeba against 19 substrates have been examined. A total of 13 enzyme complements were identified, which could be arranged in six larger groups. There was good agreement between these groupings and the arrangement of the strains that was suggested by the electrophoresis patterns of their esterases and acid phosphatases. A numericlature is described which provides an unequivocal numerical label for each enzyme complement.

Acid Phosphatase↗
PubMed1984

Mutation tests in Neurospora crassa. A report of the U.S. Environmental Protection Agency Gene-Tox Program.

Many mutation tests have been developed in Neurospora crassa during the almost 40 years of its use in mutation research. These tests detect two major classes of mutation: gene mutation and meiotic nondisjunction. Within the first class, forward- and reverse-mutation tests have been used. The forward-mutation tests include those that detect mutations at many loci and at specific loci. Both kinds of forward-mutation tests have been done in homokaryons (n) and heterokaryons (n + n'). From the publications that were not rejected by our pre-established criteria, data were extracted for 166 chemicals that had been tested for mutagenicity. Only 6 of the 166 chemicals have been tested in one or more gene mutation test and the meiotic nondisjunction test; these 6 chemicals were positive in the first and negative in the second. Of the 102 chemicals tested in one or more gene mutation tests, 94 were positive and 8 were negative. Of the 70 chemicals tested in the meiotic nondisjunction test, 7 were positive and 63 were negative. Two tests, the ad-3 forward-mutation test and the meiotic nondisjunction test, have been used most frequently. These two tests are especially important for hazard evaluation, because each detects a class of mutations that is likely to be deleterious or lethal in the F1 - disomics by the meiotic nondisjunction test and multilocus deletions by the ad-3 forward-mutation test in heterokaryons. Generally, direct-acting chemicals are mutagenic in the gene mutation tests, but few chemicals that required metabolic activation have been tested. Only 31 of the 166 chemicals tested in N. crassa have been tested for carcinogenicity. Among these chemicals, there is a good association between mutagenicity in gene mutation tests and carcinogenicity but a poorer association between meiotic nondisjunction and carcinogenicity; however, only a small number of chemicals has been tested in the meiotic nondisjunction test. Further use and development of certain mutation tests in N. crassa are desirable.

Alleles↗
PubMed1983

The cytochromes of Dictyostelium discoideum.

1. Low temperature (77 K), reduced oxidized difference spectra of "purified" mitochondria of Dictyostelium discoideum revealed the presence of b, c and a-type cytochromes. 2. The same components were also identifiable in intact organisms, the only possible discrepancies from the contribution by "microsomal" b-type cytochromes which showed major maxima at 533, 553, and 560 nm. 3. Room temperature carbon monoxide difference spectra of mitochondrial enriched fractions revealed at least three components reacting with CO. These were: cytochrome a3; another a-type cytochrome, a614; a b-type cytochrome. The latter component rapidly reacted with CO but ligand dissociation was observed over a period of about 20 min. 4. Microsomal membranes contained at least two CO-reacting components tentatively attributed to cytochromes P-450 and P-420 and it is suggested that cytochrome P-450 may be converted to cytochrome P-420 in the presence of CO and sodium dithionite. 5. The results are compared with those obtained for other protozoa.

Animals↗
PubMed1982

The structure of conversations with 6- to 10-year-old deaf children.

In stage 1 classroom conversations between sixteen teachers and their pre-lingually deaf children were videotaped and analysed to examine both the styles used by teachers in controlling conversation and the functions pursued in dialogue. In stage 2 a sub-sample of four teachers with twenty children of known hearing losses and non-verbal intelligence was analysed in greater detail to examine relationships between these factors, teaching styles and the child's performance in dialogue. The analyses show that deaf children respond in a similar fashion to young hearing children in the way they react to different styles of teacher talk; that teachers differ in the functions they pursue in conversation; and that functions change as a consequence of the child's hearing loss but not mental age. The implications of the findings for linguistic development in pre-lingually deaf children are explored.

Child↗